This invention relates generally to rotary offset printing presses and more particularly to a device for washing one or more blanket cylinders in a rotary offset press such as those of the B-B type having two opposite blanket cylinders or the satellite type having a plurality of blanket cylinders around a single impression cylinder.
In general, in a rotary offset press, after a long period of operation, foreign substances such as residual ink which has accumulated and hardened, paper dust, and clay are found to be adhering to the surface or surfaces of the blanket cylinder or cylinders. These impurities greatly impair the printing quality of the press.
As is known, a rotary offset press of the general B-B type is a perfecting press or perfector, in which a sheet of paper is passed between and pressed by a pair of blanket cylinders and thus simultaneously printed on its two surfaces, and in which a plate cylinder is in contact parallelly with each blanket cylinder on the side thereof remote from the paper. Ordinarily, the axes of the cylinders are horizontal, and one blanket cylinder is disposed above the other.
Heretofore, it has been necessary in order to wash the blanket cylinders in such a press to once stop the press and wash the surfaces of the blanket cylinders by hand. This procedure naturally results in a great loss of time and labor.
With the aim of automatizing this washing work, there has been proposed a device in which a brush roll is placed in contact with each blanket cylinder, and a washing liquid is jetted onto the blanket cylinder surface along a line in front of the position of the contact as viewed in the rotational direction of the blanket cylinder. In this device, it is desirable that each blanket cylinder and its brush roll rotate in the same direction so that their mutually facing peripheral surfaces will travel in opposite directions and that relative peripheral speed at their contact position will be high, and therefore the washing effectiveness will be high.
However, in a rotary offset press with a washing device of this character, the washing liquid tends to be slung upward from the lower blanket cylinder and to collide with the upper part of the brush roll housing, becoming droplets. A portion of these droplets drops onto the blanket cylinder and continues to drop long after completion of the washing, thereby contaminating the printing.
Another problem encountered in a washing device of the instant character is that of the drainage of the used washing liquid and accumulated impurities. More specifically, after several washings, a sludge-like substance including ink, paper dust, clay, etc., accumulates on and raises the level of the bottom of the housing. As a result of tests, it has been found that, after a number of weeks of use, the waste washing liquid, which should be drained, overflows out of the housing and impairs the printing quality. Furthermore, the work of removing the sludge-like substance is extremely troublesome.
As measures to solve this problem, it has been tried to provide the lower part of the housing with a slope and providing means for sucking out the impurities but it has been found that such measures are inadequate.